This invention relates to a video synchronizing signal separator and, more particularly, to a relatively simple yet effective separator circuit for separating the luminance and synchronizing signal components of a composite video signal.
In video signal processing circuits, such as those used in television receivers, video recorders, video signal enhancers, and the like, the usual periodic horizontal synchronizing signal that is included in the composite video signal is separated and separately processed. Desirably, the informational components of the composite video signal, such as the chrominance and luminance components, should not interfere with the separated synchronizing signal. Similarly, those informational components should be separately processed without interference from the synchronizing signal. Thus, synchronizing signal separator circuits have been developed for separating the horizontal synchronizing signal from the composite video signal.
Typical of horizontal synchronizing separator circuits heretofore used are the so-called "sync clipper" circuits formed of a diode connected in shunt with the video path, the diode being conductive to shunt the information components to ground yet being cut off in the presence of the horizontal synchronizing signal, thus passing the horizontal synchronizing signal to further circuitry. A similar diode has been used to clamp the informational components, and particularly the luminance signal, to a predetermined level, such as the black level. This clamping diode is conductive to shunt the synchronizing signal to ground.
Although the aforementioned sync clipper circuits have proven to be successful in operation and are relatively inexpensive, there have been proposals for more complicated sync processing circuits, such as described in U.S. Pat. Nos. 3,881,055, 4,057,826, 4,424,528 and 4,453,183.
It is desirable to provide a sync separator circuit of relatively simple and inexpensive construction, yet is reliable in separating the synchronizing signal component from its composite video signal.